The present invention relates to a system for controlling an electro-magnetic clutch for automobiles, and more particularly to a system for controlling an electro-magnetic powder clutch which is capable of eliminating residual magnetism.
An electro-magnetic powder clutch comprises an annular drive member secured to the crankshaft of the engine, a magnetizing coil provided in the drive member, a driven member secured to the input shaft of the transmission spaced by a gap from the drive member, powder provided in the clutch, and a shift lever for changing gears in the transmission. The shift lever is provided with a switch for the magnetizing coil, which is actuated by operating the shift lever. When the shift lever is shifted to a gear engaging position, the switch is closed so that electric current flows through the magnetizing coil to magnetize the drive member. As the accelerator pedal is depressed, the current applied to the coil increases. The powder in the clutch is aggregated in the gap by the magnetic flux, so that the driven member is coupled to the drive member through the powder. Thus, the output of the engine may be transmitted to the transmission. In such an electromagnetic clutch, in order to achieve smooth engagement between gears in the transmission, the system is adapted to cause the clutch to actuate a so-called double-clutch action. That is, the switch is so arranged that it is closed for magnetizing the coil when the shift lever is in the neutral position, and it is opened when a manual operating force is applied to the shift lever for changing speed. Thus, the clutch is engaged in the neutral position and is disengaged during the operation of the shift lever, and is engaged again when the shift lever reaches the gear engaging position.
In such a system, when the shift lever is shifted from one change speed position to another change speed position passing through the neutral position, residual magnetism occurs in the clutch. The shift lever then must be operated against the drag torque caused by the residual magnetism, which requires a great manual operating force. This tendency increases when the engine speed is increased at idling. In a transmission without a synchronizing mechanism, when the gear-change is quickly performed, gears do not smoothly engage each other, because it takes a long time until the gears are synchronized.